PROJECT SUMMARY Enteric bacterial infections remain one of the greatest public health challenges worldwide and deciphering the mechanisms that protect against infection will enable development of new treatments. Intestinal tissues are in constant direct contact with diverse beneficial and pathogenic microbes, highlighting the need for orchestrating complex microbial signals to sustain protection against infection. Intestinal epithelial cells (IECs) reside at the direct interface between intestinal pathogens, beneficial commensal bacteria, and intestinal immune components. However, despite continuous exposure to diverse microbes, the mechanisms regulating how IECs integrate microbial-derived signals to mount protective host responses to pathogens are not well understood. Epigenetic changes represent a powerful interface that enable cells to respond to environmental signals and modify gene expression. The goals of this proposal are to interrogate how specific commensal bacterial-derived metabolites that regulate the epigenetic-modifying enzyme histone deacetylase 3 (HDAC3) influence intestinal protection against infection and bacterial translocation. Employing Citrobacter rodentium, a murine model of human enteropathogenic Escherichia coli infection, our studies identified that HDAC3 protects against enteric bacterial infection. New preliminary data suggest commensal bacterial-derived metabolites can directly modulate HDAC3 function in IECs and that distinct types of commensal bacteria establish unique histone acetylation signatures in IECs. Collectively, these data suggest that HDAC3 senses distinct metabolite signals derived from commensal bacteria to epigenetically prime host defense against pathogenic bacterial infection. Employing an exciting array of transgenic animals, pathogenic and commensal bacterial strains, and human intestinal organoids, three specific aims are proposed that will (i) investigate metabolite-dependent regulation of enteric infection, (ii) decipher how the host calibrates intestinal barrier function by sensing distinct commensal bacterial-derived metabolites, and (iii) interrogate whether distinct types of commensal bacteria prime the epigenome to enhance host response to pathogenic bacteria. Defining pathways that integrate commensal and pathogenic signals will provide a framework to test the therapeutic potential of manipulating commensal bacterial-derived metabolites to promote antibacterial immunity.